JS check if an array is embedded in another array

Question

I have a two dimensional JS array in which some rows are useless and needs to be deleted; In particular I need to delete the rows that are embedded in other rows (by saying that row B is embedded in row A I mean not just that A is a superset of B, but that A contains all the elements in B, in sequence and in the same order)

EX. I have:

var matrix = [
    ["User","Shop","Offer","Product","File"],            
    ["User","Shop","File"],
    ["User","Shop","Map"],
    ["User","Shop","Promotion"],
    ["User","Shop","Offer","Product","Reservation"],
    ["User","Group","Accesslevel"],
    ["User","Group"],
    ["User","Reservation"],
    ["User","Shop"],
    ["User","Shop","Offer","Product","Markers"]
];

In this example the second row (["User","Shop","File"]) should NOT be deleted (all its elements are in the first row, but not consecutive);

Row 7 (["User","Group"]) should be deleted because is embedded in the 6th (["User","Group","Accesslevel"]) and also row 9 (["User","Shop"]) because is embedded in many others..

I'm looking for a possible efficient algorithm to check if an array is embedded in another one; I will use this in nodejs.

It's unclear if you're looking for just the same occurrences, so that you have unique strings in each array or if are trying to find the same sequences, and if so, what is the minimum number of strings in that sequence, does the order have to be the same, etc. — inorganik
– inorganik, Commented Oct 13, 2014 at 14:37
You could make some sort of recursive function that checks every property in every object, starting with window. Then, if it is an array, check if your array is in that array and return true if yes, and if it never finds your array return false. It would be expensive though. — Nick Manning
– Nick Manning, Commented Oct 13, 2014 at 14:38
As you're looking for them in sequence, you could join() each sub array into a string and run a regex match on them, testing each to every other string. Can't say if it's fast but it's easy enough — caffeinated.tech
– caffeinated.tech, Commented Oct 13, 2014 at 14:38
@inorganik: "I mean not just that A is a superset of B, but that A contains all the elements in B, in sequence and in the same order" — Felix Kling
– Felix Kling, Commented Oct 13, 2014 at 14:39
@inorganik I try to explain better: I need to check if every row is embedded in any other (once found that is embedded in another, can be removed); of course a row with 5 elements cannot be embedded in a row with less than 5; I need the same sequence and the same order — Cereal Killer
– Cereal Killer, Commented Oct 13, 2014 at 14:41

score 1 · Accepted Answer · 2014-10-13 18:46:01Z

1

This should do the trick.

// Is row2 "embedded" in row1?
function embedded(row1, row2) {
    return row2.length < row1.length &&
        row2.every(function(elt, i) { return elt === row1[i]; });
}

//filter out rows in matrix which are "embedded" in other rows
matrix.filter(function(row) {
    return !matrix.some(function(row2) { return embedded(row2, row); });
});

edited Oct 13, 2014 at 18:46

answered Oct 13, 2014 at 18:38

user663031

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2 Comments

mplungjan Over a year ago

Very elegant - compatibility with older browsers?

user663031 Over a year ago

You can use (and probably already should be using) shims/polyfills for Array#{every, some, filter}. Failing that, the above could be rewritten in the obvious way using Underscore equivalents.

Naeem Shaikh · Accepted Answer · 2014-10-13 15:32:22Z

1

here is a solution which I used few days ago for the same purpose but on the client side, This would also work on node server. http://jsfiddle.net/8wLst3qr/ I have changed the program according to your needs,

What I have done here is,

some initialisation,

var matrix = [
    ["User","Shop","Offer","Product","File"],            
    ["User","Shop","File"],
    ["User","Shop","Map"],
    ["User","Shop","Promotion"],
    ["User","Shop","Offer","Product","Reservation"],
    ["User","Group","Accesslevel"],
    ["User","Group"],
    ["User","Reservation"],
    ["User","Shop"],
    ["User","Shop","Offer","Product","Markers"]
];

var tempArr=matrix;

here are the steps

convert the array of arrays to an array of strings-(this is because you need to clear the redundant data only if it is in the same order), code as follows.

var json=[];

    for(k=0;k<tempArr.length;k++)
        {
       json[k]=tempArr[k].toString();

        }

and then match the index of each string in other strings in the array, if matches, check the string whose length is less and delete it.

for(k=0;k<json.length;k++)
    {
        for(l=0;l<json.length;l++)
            {
                        console.log("val l="+json[l]+"val k="+json[k]+"value="+json[l].indexOf(json[k])); 
                console.log("k="+k+";l="+l);
               if(k!=l && (json[k].indexOf(json[l]) !=-1))
               {
                      console.log("removing");
                   console.log("removing");
                   if(json[k].length>json[l].length)
                   {
                       json.splice(l, 1);
                   }
                   else
                   {
                       json.splice(k, 1);
                   }
               }
            }

    }

hope it helps,

edit-sorry you would require to check the console.log for the output on fiddle

answered Oct 13, 2014 at 15:32

Naeem Shaikh

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2 Comments

Cereal Killer Over a year ago

This works good; thanks for help; Probably if you need to do this often and/or on large arrays, could be possible to find a more efficient algorithm since this one is quadratic; in my case I need to do this only once, when server starts, so it is more than enough

mplungjan Over a year ago

Also be aware that toString may not work correctly in cases where there are words that match longer words - I suggest to compare "|"+matrix[i].join("|")+"|"

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